The properties of whey protein -carrageenan mixtures during the formation of electrostatic coupled biopolymer and emulsion gels

•WPI-CG mixtures formed electrostatic coupled networks, regardless of the CG type.•The gel point in WPI-CG mixtures corresponds to complex coacervation pH.•Protein-stabilized emulsion coupled networks were formed for all mixed systems.•Networks formed with kappa-CG and iota-CG were stronger than those with lambda-CG.

The rheological properties of whey protein isolate (WPI) and WPI with carrageenan (CG) (kappa-, iota- and lambda-types) mixtures during a slow acidification process were investigated in a non-emulsified and emulsified system. For all systems, electrostatically coupled networks were formed leading to the formation of a biopolymer or emulsion-based gel network. However, network strength differed depending on the CG-type. In the case of biopolymer gels, the storage modulus within the plateau zone for WPI-kappa-CG and WPI-iota-CG mixtures were ~ 93 and ~ 73 Pa, respectively, whereas the WPI-lambda-CG network was weaker (~ 8 Pa). The gel point corresponded to the pH where complex coacervation occurred. WPI-CG mixtures were also able to lower interfacial tension from 28 to 18-22 mN/m before gelation. Emulsion gels followed a similar trend as the biopolymer networks, except they were stronger (WPI-kappa-CG, WPI-iota-CG and WPI-lambda-CG systems had storage moduli of ~ 435, ~ 320 Pa and ~ 103 Pa, respectively). The presence of CG decreased the average droplet size of these emulsions from ~ 38 to ~ 32 μm, regardless of the CG type. Protein stabilized emulsion gels were presumed to form, where upon complexation with CG, flocculation between droplets was promoted until an electrostatic-stabilized gel network was formed within the continuous phase. The WPI control did not gel for both non-emulsified and emulsified systems.